Installing Kohler Shower Drain Gasket

I have a Kohler K-9132 shower drain I'm trying to install. The last step is to install the big gasket that makes the seal between the drain housing and drain pipe. I got this gasket about 3/4 of the way inserted, still have about a half an inch to go and it will not move anymore. The whole "soapy water lubricant" thing in the instructions didn't seem to help much. I've tried working it with a wood shim, but I've gotten as far as she'll go it seems.

Any advice? Is there enough in there for a good seal and I can just trim off the last half inch?

Well, still no-go. The blunt screwdriver would penetrate the gasket; tried a square nail, but the gasket would just absorb the hammer blows and bounce back. Pushing on it just compresses the top of the gasket, making it thicker and even more impossible to push in.

Oh well, I guess I'll just have to take my chances and if it leaks, then I'll by a drain that has some kind of a threaded retainer that pushes the gasket in. Didn't think I'd have to worry about this sort of thing buying a Kohler drain. Customer service there didn't have any ideas other than what was in the instructions.